1. Field of the Invention
The present invention relates to a microlens array typically used in the fields of optical communication and optical packaging for coupling light emitted from a light source to an optical fiber or an optical waveguide, converting light emitted from the optical fiber or the optical waveguide into parallel rays or so focusing light beams to enter the optical fiber or the optical waveguide in an optical coupling system.
2. Related Art of the Invention
The microlens in general represents a fine lens having a lens diameter of not more than a several millimeters. Various methods relating to the microlens array including methods for manufacturing the same have been proposed in the art. The ion exchange diffusion method is widely known as a method for manufacturing the microlens array. In the ion exchange diffusion method, a dopant ion is selectively diffused on a multicomponent glass substrate.
The conventional ion exchange diffusion method will be described below with reference to FIGS. 14A to 14C. As shown in FIG. 14A, an ion exchange control membrane 102 is firstly formed on a surface of a multicomponent glass substrate 101 containing a monovalent ion. The ion exchange control membrane 102 may be a metal membrane or a dielectric membrane. Next, an array of circular apertures 103 at a predetermined pitch that is equivalent to that of an LD array or a PD array is formed on the ion exchange control membrane 102 using a photolithographic technique or a etching technique. The diameter of a lens prepared according to this method is determined by each of the apertures 103, and the apertures function as light-shielding membrans for reducing crosstalk between adjacent channels.
High temperature molten salt 104 shown in FIG. 14B containing a dopant ion that will contribute to ascending in refractive index. The dopant ion may include Tl, Ag and Pb, each having a high degree of refractive index. Then, the glass substrate 101 that is coated with the ion exchange control membrane 102 having the circular apertures 103 is immersed in the molten salt 104 so that the dopant ion is selectively diffused on the glass substrate 101 through the apertures 103 on the ion exchange control membrane 102 to thereby form ion exchange areas 105 each having a hemispheric diffusion front. The ion exchange areas 105 serve as distributed refraction type lenses according to a dopant ion distribution. Here, as a result of selecting the dopant ion having the ion radius that is larger than that of the ion contained in the glass substrate 101, the surface of the substrate 101 is expanded according to the volumetric difference between the ions to form convex lenses 106 shown in FIG. 14C. A diameter of each of the convex lenses 106 is typically in a range of from a several tens of microns to a several hundreds of microns.
The above-illustrated ion exchange diffusion method is suitable for forming a microlens having a diameter of from a several tens of microns to a several hundreds of microns; however, problems have been found with the method in manufacture of a microlens having a relatively large lens diameter or a lens effective diameter of from a several hundreds of microns to a several millimeters. More specifically, in order to prepare the relatively large microlens employing the ion exchange diffusion method, a depth of the diffusion must be a several hundreds of microns or more that is about the same as the size of the lens to be produced and it is necessary to conduct a heat treatment at a high temperature for a remarkably long time. Thus, in the ion exchange diffusion method, it is difficult to prepare lenses of a wide range of sizes having diameters from a several tens of microns to a several millimeters and, also, it is impossible to produce a microlens array having a focal length that is about the same as that of the diameter of the lens. Therefore, downsized and high-performance optical coupling elements have not been realized by the use of the ion exchange diffusion method.
In view of the above problems, an object of the present invention is to provide a method of manufacturing a microlens array that realizes downsized and high-performance optical coupling elements to be used in the fields of optical communication and optical packaging.
One aspect of the present invention is a method of manufacturing a microlens array comprising forming microlenses by dropping or injecting to a plurality of through holes formed on a substrate a liquefied lens material so as to dispose the lens material at each of the through holes, the lens material being curable and has a predetermined transmittivity and a predetermined viscosity.
Another aspect of the present invention is the method of manufacturing a microlens array, wherein a curvature of each of the microlens is varied by adjusting whole or part of (1) configurations or sizes of the through holes of the substrate, (2) wettability between the substrate and the lens material, (3) a viscosity of the lens material and (4) a quantity of lens material in a droplet or in an injection shot.
Still another aspect of the present invention is the method of manufacturing a microlens array, wherein the lens material is dropped or injected substantially simultaneously by using nozzles that can drop or inject the lens material substantially simultaneously to the through holes.
Yet still another aspect of the present invention is the method of manufacturing a microlens array, wherein the lens material is a ultraviolet ray curable resin material, a thermosetting resin material, a thermoplastic material or a glass material.
Still yet another aspect of the present invention is the method of manufacturing a microlens array according to 1st invention, wherein each of the through holes has a truncated conical shape or a step portion.
A further aspect of the present invention is the method of manufacturing a microlens array, wherein the microlenses are convex lenses.
A still further aspect of the present invention is the method of manufacturing a microlens array according to 1st invention, wherein the microlenses are concave lenses.
A yet further aspect of the present invention is the method of manufacturing a microlens array, wherein all refractive indexes and/or a transmittivities of the lens materials to be dropped or injected to the plurality of through holes are not same.
A still yet further aspect of the present invention is the method of manufacturing a microlens array, wherein a whole or a part of the plurality of through holes vary in size, and the lens material is dropped or injected in accordance with the sizes of the through holes.
An additional aspect of the present invention is the method of manufacturing a microlens array, wherein the plurality of through holes are arranged on the substrate to give a closest packed structure, each of the through holes having the shape of a hexagon of a predetermined size.
A still additional aspect of the present invention is the method of manufacturing a microlens array, wherein the substrate is formed from silicone, a plastic material, a glass material, ceramic material, fiber material or a composite material.
A yet additional aspect of the present invention is a microlens multilayer formed by laminating a plurality of microlens arrays produced by the method of manufacturing a microlens array according to any one of 1st to 11th inventions, wherein the plurality of microlens arrays are so laminated that optical axes of the microlenses of each microlens array coincide with the optical axes of the corresponding microlenses of another microlens array.
A still yet additional aspect of the present invention is a microlens array comprising a substrate in which a plurality of through holes are formed and a plurality of microlenses respectively disposed at the through holes in the substrate, wherein
the microlenses are fixed to the through holes of the substrate by way of adhesion or deposition of a microlens material to a substrate material.
A supplementary aspect of the present invention is the microlens array, wherein the microlenses are formed of a ultraviolet ray curable resin material, a thermosetting resin material, a thermoplastic material or a glass material.
A still supplementary aspect of the present invention is the method of manufacturing a microlens array, wherein each of the through holes has a truncated conical shape or a step portion.
A yet supplementary aspect of the present invention is the method of manufacturing a microlens array, wherein the microlenses are convex lenses.
A still yet supplementary aspect of the present invention is the method of manufacturing a microlens array, wherein the microlenses are concave lenses.
Another aspect of the present invention is the method of manufacturing a microlens array, wherein all refractive indexes and/or a transmittivities of the lens material to be dropped or injected to the plurality of through holes are not same.
Still another aspect of the present invention is the method of manufacturing a microlens array, wherein a whole or a part of the plurality of through holes vary in size and a whole or a part of the microlenses vary in size in accordance with the sizes of the through holes.
Yet still another aspect of the present invention is the method of manufacturing a microlens array, wherein the plurality of through holes are arranged in the substrate to give a closest packed structure, each of the through holes having the shape of a hexagon of a predetermined size.
Still yet another aspect of the present invention is the method of manufacturing a microlens array, wherein the substrate is formed of any one of silicone, a thermoplastic material, a glass material, a ceramic material, a fiber material and a composite material.
A further aspect of the present invention is the method of manufacturing a microlens array, wherein each of the microlenses has a multilayer structure that consists of a plurality of layers varying in material and refractive index.
A still further aspect of the present invention is the method of manufacturing a microlens array, wherein each of the plurality of through holes in the substrate has a rectangular shape of a predetermined size and each of the microlenses that is formed by dropping has an anamorphotic or cylindrical configuration.
A yet further aspect of the present invention is the method of manufacturing a microlens array, comprising subjecting a surface of the substrate to an inactivating treatment so that a portion of the surface excluding the through holes has repelling properties to the lens material and the through holes have adhesive properties to the lens material.
A still yet further aspect of the present invention is the method of manufacturing a microlens array, wherein the surface of the substrate is caused to be uneven by the inactivating treatment.